Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

Cathode materials for use in thermal batteries are disclosed. The cathode
material includes a primary active material and an amount of a bi-metal
sulfide such as CuFeS2. Batteries (e.g., thermal batteries) that
contain such cathode materials are also disclosed.

Claims:

1. A cathode material for use in thermal batteries, the cathode material
comprising:at least one of a metal sulfide and a metal oxide; anda
bi-metal sulfide.

2. The cathode material as set forth in claim 1 wherein the cathode
material comprises a metal sulfide selected from the group consisting of
FeS2, CoS2 and mixtures thereof.

3. The cathode material as set forth in claim 1 wherein the bi-metal
sulfide is CuFeS.sub.2.

4. The cathode material as set forth in claim 1 wherein the cathode
material comprises an amount of electrolyte material.

5. The cathode material as set forth in claim 4 wherein the cathode
material comprises:at least about 46 wt % of a metal sulfide selected
from the group consisting of FeS2, CoS2 and mixtures thereof;
andat least about 2 wt % CuFeS.sub.2.

6. The cathode material as set forth in claim 5 wherein the cathode
material comprises:no more than about 80 wt % of a metal sulfide selected
from the group consisting of FeS2, CoS2 and mixtures thereof;
andno more than about 14 wt % CuFeS.sub.2.

7. The cathode material as set forth in claim 5 wherein the cathode
material comprises at least about 6 wt % CuFeS.sub.2.

9. The cathode material as set forth in claim 1 wherein the cathode
material comprises:at least about 76 wt % of a metal sulfide selected
from the group consisting of FeS2, CoS2 and mixtures thereof;
andat least about 2 wt % CuFeS.sub.2.

10. The cathode material as set forth in claim 9 wherein the cathode
material comprises at least about 9 wt % CuFeS.sub.2.

11. The cathode material as set forth in claim 1 wherein the CuFeS2
is synthetic or is obtained from chalcopyrite.

12. The cathode material as set forth in claim 1 wherein the cathode
material comprises at least about 1 wt % LiO.sub.2.

14. The battery as set forth in claim 13 wherein the cathode material
comprises a metal sulfide selected from the group consisting FeS2,
CoS2 and mixtures thereof.

15. The battery as set forth in claim 13 wherein the bi-metal sulfide is
CuFeS.sub.2.

16. The battery as set forth in claim 13 wherein the cathode material
comprises an amount of the electrolyte material.

17. The battery as set forth in claim 16 wherein the cathode material
comprises:at least about 46 wt % of a metal sulfide selected from the
group consisting of FeS2, CoS2 and mixtures thereof; andat
least about 2 wt % CuFeS.sub.2.

18. The battery as set forth in claim 17 wherein the cathode material
comprises:no more than about 80 wt % of a metal sulfide selected from the
group consisting of FeS2, CoS2 and mixtures thereof; andno more
than about 14 wt % CuFeS.sub.2.

19. The battery as set forth in claim 17 wherein the cathode material
comprises at least about 6 wt % CuFeS.sub.2.

20. The battery as set forth in claim 13 wherein the CuFeS2 is
synthetic or is obtained from chalcopyrite.

22. The battery as set forth in claim 21 wherein the electrolyte material
is substantially binder-free.

23. The battery as set forth in claim 21 wherein the electrolyte material
is substantially MgO-free.

24. The battery as set forth in claim 21 wherein the lithium bromide,
lithium chloride, lithium fluoride and potassium bromide form a eutectic
mixture.

25. The battery as set forth in claim 21 wherein the electrolyte material
comprises:no more than about 41 wt % lithium bromide;no more than about
14 wt % lithium chloride;no more than about 64 wt % lithium fluoride;
andno more than about 12 wt % potassium bromide.

26. The battery as set forth in claim 13 wherein the cathode material
comprises at least about 1 wt % LiO.sub.2.

27. The battery as set forth in claim 13 wherein the battery is a thermal
battery and comprises pyrotechnic material.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This application claims the benefit of U.S. Provisional Application
No. 61/167,042, filed Apr. 6, 2009, which is incorporated by reference
herein in its entirety.

BACKGROUND

[0002]The field of this disclosure generally relates to cathode material
for use in thermal batteries and, particularly, to cathode material that
includes a primary active material and an amount of a bi-metal sulfide
such as, for example, CuFeS2. The disclosure also relates to
batteries (e.g., thermal batteries) that contain such cathode materials.

[0003]Thermal batteries tend to have relatively long shelf lives, high
energy densities, require relatively low maintenance, and can withstand
relatively high temperatures. Thermal batteries also tend to provide a
short burst of power over a relatively short period of time. The burst
may range from less than a second to an hour or more, with power
typically ranging from about a watt or less to kilowatts. Such properties
make thermal batteries suitable for military (e.g., batteries for missile
guidance systems) and space exploration applications. Thermal batteries
may also be used in other applications, such as in electric vehicles.

[0004]A typical thermal battery includes an anode, a cathode, an
electrolyte-separator containing a solid electrolyte that is
non-conductive at ambient temperature, and a pyrotechnic material (e.g.,
heat pellet as in FIG. 1 which may contain, for example, Fe--KClO4
powder) that provides a heat source to the battery. When battery
operation is desired, an external stimulus is applied to the battery. For
example, an electrical current may be applied to the battery to set off
an electric match or an electro-active squib or a mechanical force (e.g.,
mechanical shock) may be applied to set off a concussion primer. The
external stimulus causes the pyrotechnic material to ignite and begin to
heat. Heat produced from the pyrotechnic material causes the previously
solid electrolyte to melt and become conductive, which allows the battery
to provide power for a desired application.

[0005]Thermal batteries are often formed using pellet techniques, such
that each of the electrolyte, cathode, and heat source are formed into a
wafer. In this case, the respective cell component chemicals are
processed into powders and the powders are pressed together to form the
cell. Each component may be formed as a discrete part, or the anode
and/or cathode may include (i.e., be flooded with) electrolyte material
to improve the conductivity of the cell.

[0006]The anodes of thermal batteries are generally formed of an alkali or
alkaline earth metal or alloy. A typical anode includes lithium metal or
a lithium alloy, such as lithium aluminum, lithium silicon, or lithium
boron.

[0007]Electrolytes for use with thermal batteries often include a eutectic
mixture (i.e., a mixture which solidifies at a temperature lower than
each of the individual components) of lithium chloride and potassium
chloride and a binder, such as MgO, fumed silica or clay minerals such as
kaolinite (including kaolin clays which are known to be rich in
kaolinite), which assists in containing the electrolyte within the
thermal battery assembly such as by capillary action, surface tension, or
both. The electrolyte-separator is often composed of binary or ternary
salts melting at temperatures above ambient between 200° C. and
600° C. With typical thermal battery electrolytes, without
sufficient binder, the electrolyte material may disperse throughout the
battery, causing undesired shunts or short circuits in the cell.

[0008]Cathode material for thermal batteries may vary in accordance with a
variety of design parameters and generally includes a metal oxide or
metal sulfide. By way of example, iron oxide, iron disulfide or cobalt
disulfide are often used as cathode material.

[0009]Typical thermal batteries make use of what is essentially a
monolithic cathode material. While the cathode may contain components
other than active cathode material such as, for example, the electrolyte
to provide flooding and a lithiation additive (i.e., a lithium compound
other than a lithium salt) to control voltage, conventionally there is
only one active material such as, for example, a metal oxide (e.g.,
FeO4) or metal sulfide (e.g., CoS2 or FeS2). Some research
has been performed on incorporating additives of other sulfides to
provide improved performance, such as Walsh et al. in U.S. Pat. No.
3,992,222, who examined FeS2 cathodes incorporating a second sulfide
as an additive to result in improved performance. The sulfides that were
examined, however, were limited to single metal sulfides, such as
titanium disulfide, nickel sulfide, or cerium sulfide.

[0010]A continuing need therefore exists for cathode materials that
contain additives that result in improvements in conductivity, voltage
and lifetime. A continuing need also exists for thermal batteries that
incorporate such cathode materials and that exhibit such improved
performance.

SUMMARY

[0011]The present disclosure provides improved cathode material for use in
thermal batteries and batteries including the material. Cathodes in
accordance with the present disclosure and batteries containing such
cathodes are generally characterized by enhanced conductivity, increased
voltage, and/or longer lifetime as compared to conventional cathodes and
batteries.

[0012]In one aspect of the present disclosure, a cathode material for use
in thermal batteries includes at least one of a metal sulfide and a metal
oxide. The cathode material also includes a bi-metal sulfide.

[0013]In another aspect of the present disclosure, a battery includes
anode material, cathode material, and electrolyte material. The cathode
material contains at least one of a metal sulfide and a metal oxide. The
cathode material also contains a bi-metal sulfide.

[0014]Various refinements exist of the features noted in relation to the
above-mentioned aspects of the present disclosure. Further features may
also be incorporated in the above-mentioned aspects of the present
disclosure as well. These refinements and additional features may exist
individually or in any combination. For instance, various features
discussed below in relation to any of the illustrated embodiments of the
present disclosure may be incorporated into any of the above-described
aspects of the present disclosure, alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]A more complete understanding of the present disclosure may be
derived by referring to the detailed description and claims, considered
in connection with the figures, wherein like reference numbers refer to
similar elements throughout the figures, and:

[0016]FIG. 1 illustrates an electrochemical device in accordance with
various embodiments of the present disclosure.

[0017]FIG. 2 illustrates a voltage trace diagram of a thermal battery cell
in accordance with a first embodiment of the disclosure and a trace
diagram of a conventional cell.

[0018]FIG. 3 illustrates an impedance trace of a thermal battery cell in
accordance with the first embodiment of the disclosure and a conventional
cell.

[0019]FIG. 4 illustrates a voltage trace of a thermal battery cell in
accordance with a second embodiment of the disclosure and a conventional
cell.

[0020]FIG. 5 illustrates an impedance trace of a thermal battery cell in
accordance with the second embodiment of the disclosure and a
conventional cell.

[0021]FIG. 6 illustrates a voltage trace of a thermal battery cell formed
in accordance with a third embodiment of the disclosure and a
conventional cell.

[0022]FIG. 7 illustrates an impedance trace of a thermal battery cell in
accordance with the third embodiment of the disclosure and a conventional
cell.

[0023]Corresponding reference characters indicate corresponding parts
throughout the drawings. It should be noted that elements in the figures
are illustrated for simplicity and clarity and have not necessarily been
drawn to scale. For example, the dimensions of some of the elements in
the figures may be exaggerated relative to other elements to help to
improve understanding of embodiments of the present disclosure.

DETAILED DESCRIPTION

[0024]The present disclosure generally relates to improved thermal battery
cathode formulations and to batteries including the cathode material.
FIG. 1 illustrates a thermal battery 100 that has an exemplary
configuration suitable for use in thermal batteries of the present
disclosure. The thermal battery includes an anode 102, an
electrolyte-separator (electrolyte) 104, and a cathode 106. In accordance
with the present disclosure, the cathode material may include a bi-metal
sulfide additive. As set forth in more detail below, the addition of the
bi-metal sulfide additive to the cathode material (e.g., FeO4,
FeS2 or CoS2) results in improved cell performance.

[0025]As used herein, an "electrochemical device" may otherwise be
referred to as a battery (and in some embodiments, a "thermal battery"),
a capacitor, a cell, an electrochemical cell, or the like. It should be
understood that these references are not limiting, and any device that
involves electron transfer between an electrode and an electrolyte is
contemplated within the scope of the present disclosure. Further, an
electrochemical device may refer to single or multiple connected
electrochemical devices, electrochemical cells, batteries or capacitors
capable of supplying energy to a load, and none of the references herein
to any particular device should be considered to limit the disclosure in
any way.

[0026]In accordance with various embodiments of the disclosure, cathode
materials for use in thermal batteries are prepared by consolidating
powders via a mechanical pressing operation or other powder handling
means, such as tape casting, to produce pellets (i.e., wafers). The
pellets are then stacked in a desired arrangement to provide voltage and
current when the battery is activated.

[0027]A primary active material for cathode is a metal oxide such as
FeO4 or a metal sulfide such as FeS2, CoS2 or mixtures
thereof. In this regard, it should be understood that combinations of
metal oxides and metal sulfides may be used in any relative proportion
without limitation.

[0028]In accordance with the present disclosure, the primary active
material may be combined with a secondary active material which is
typically a bi-metal sulfide such as, for example, CuFeS2, to
enhance the conductivity, increase voltage, and/or lengthen the lifetime
of batteries that include the cathode. The source of bi-metal sulfide
material (e.g., CuFeS2) may be a natural mineralogical source (e.g.,
chalcopyrite) or the bi-metal sulfide material may be synthetically
produced by any of the methods known to those of skill in the art. The
cathode material may also contain an amount of lithium such as Li2O
to regulate the battery voltage (e.g., at least about 1 wt % or from
about 1 wt % to about 5 wt % Li2O).

[0029]The composition of the cathode material may vary in accordance with
the desired cell application. Exemplary, non-limiting, compositions for
cathode material are set forth below.

[0030]In this regard, it should be noted that, more generally, the cathode
material may contain, in various exemplary embodiments: at least about 46
wt % of the first metal compound (e.g., FeO4, FeS2 or
CoS2), at least about 50 wt %, at least about 55 wt %, at least
about 60 wt %, at least about 65 wt %, at least about 70 wt % or even at
least about 75 wt % of the first metal compound; at least about 2 wt % of
the bi-metal sulfide (e.g., CuFeS2), at least about 5 wt %, at least
about 8 wt % or even at least about 11 wt % of the bi-metal sulfide; at
least about 20 wt % of the electrolyte material, at least about 24 wt %,
at least about 28 wt %, at least about 32 wt % or even at least about 36
wt % of the electrolyte material; and, optionally, at least about 1%
lithiation additive or at least about 3 wt % lithiation additive. It is
to be further noted that, in these or other exemplary embodiments, the
cathode material may contain: no more than 80 wt % of the first metal
compound, no more than about 14 wt % of the bi-metal sulfide, no more
than about 40 wt % of the electrolyte material and, when present, no more
than about 5 wt % of the lithiation additive. In addition, it is to be
noted that, in one or more of the embodiments detailed herein, the
concentration of a recited component may be within a range bounded by any
combination or permutation of the higher and lower concentration limits
noted herein (e.g., between about 2 wt % and about 14 wt % or between
about 5 wt % and about 14 wt % of bi-metal sulfide), without departing
from the intended scope of the present disclosure.

[0031]Furthermore, in this regard it should be noted that, since the
cathode of the thermal batteries of the present disclosure typically
contains flooded electrolyte, the components of the cathode material are
typically expressed throughout the specification (e.g., as in Table 1
above and the proceeding paragraph) as a percentage of the total amount
of active cathode materials, electrolyte materials and lithiation
additives (if any). Additionally, or alternatively, it should also be
understood that, in some embodiments, the cathode does not contain
electrolyte material (e.g., only the anode contains flooded electrolyte)
and/or does not contain lithiation additives. For instance, if the
cathode materials of Table 1 above did not contain electrolyte or
lithiation additive, the cathode materials may have the following
exemplary, non-limiting compositions.

[0032]In this regard, more generally in exemplary embodiments in which the
electrode material does not contain electrolytes or lithiation additives,
the cathode material may contain at least about 76 wt % of the first
metal compound, at least about 80 wt %, at least about 85 wt %, at least
about 90 wt % or at least about 95 wt % of the first metal compound. In
these and other embodiments, the cathode material may contain at least
about 2 wt % bi-metal sulfide, at least about 5 wt %, at least about 10
wt %, at least about 15 wt % or even at least about 20 wt % bi-metal
sulfide. It should be further noted that, in these and other exemplary
embodiments, the cathode material may contain no more than about 98 wt %
of the first metal compound and may contain no more than about 24 wt % of
the bi-metal sulfide. As expressed above, the concentration of a recited
component may be within a range bounded by any combination or permutation
of the higher and lower concentration limits noted herein without
limitation.

[0033]Accordingly, in these or in other embodiments in which the cathode
material does not contain electrolyte material or lithiation additives,
the cathode material may consist of the recited components (e.g., the
first metal compound and bi-metal sulfide) or, alternatively, consist
essentially of these components (i.e., may include other compounds but
exclude electrolyte materials, lithiation additives and all other active
cathode materials). Further, in embodiments described above in which the
cathode material includes a first metal compound, a bi-metal sulfide,
electrolyte material and, optionally, lithiation additives, the cathode
material may consist of these compounds or, alternatively, consist
essentially of these compounds (e.g., exclude active cathode compounds
other than the first metal compound and the bi-metal sulfide).

[0034]An electrolyte that is suitable to flood the cathode and enable
longer life from the cell may be prepared by mixing the salts, for
example, potassium chloride (KCl) and lithium chloride (LiCl) eutectic,
with a binder material such as MgO and fusing the salts above their
liquidus temperature (e.g., at least about 500° C. or even at
least about 650° C.). The fused salt-binder mixture is ground and
sieved to restrict the particle size distribution. Generally, the size of
the particles of the electrolyte material is not critical; however, the
particle size should be consistent with typical battery manufacturing
operations as dependent on the battery design as appreciated by those of
skill in the art. For example, tape casting methods generally use smaller
particles than pellet pressing methods. When pellet pressing methods are
used to form the electrolyte material (such as when the electrolyte
material is used to flood a cathode or anode), the electrolyte particles
should be screened such that they are sufficiently small to allow proper
filling of the die but yet large enough such that they do not infiltrate
the gap between the punch and the die. In tape casting methods, the
particles should be sufficiently small to allow casting of a thin tape.
Suitable particle size ranges may be readily determined by those of skill
in the art.

[0035]The starting salt materials may be either in powder or granulated
form and are preferably dried at a temperature sufficient to remove an
amount of absorbed moisture (if any). Moisture may be removed as much as
economically practical and as much as practical in view of the selected
manufacturing process. Generally, the amount of moisture should be
reduced to an amount that does not cause an unacceptable amount of anode
material oxidation. In some embodiments of the present disclosure, the
electrolyte salt material may be heated, for example to a temperature of
from about 100° C. to about 400° C., to remove moisture
from the material.

[0036]If desired, a lithiation additive, such as lithium oxide (Li2O)
may be added to the electrolyte material to provide voltage regulation by
limiting the peak voltage of the cell.

[0037]In preparing the battery components, the constituents (e.g.,
electrolyte salts, first metal compound and bi-metal sulfide) are weighed
out in the appropriate ratio, such as ratios consistent with compositions
described above, and mixed to obtain a homogeneous powder. The first
metal compound and bi-metal sulfide may be added directly to the
electrolyte salt material or, alternatively, the first metal compound and
bi-metal sulfide may first be combined and mixed and then added and mixed
with the electrolyte material. Physical mixing may proceed via any
mechanical mixing method, for example, stirring the salts by hand,
agitating the ingredients in a Turbula blender, rolling the container on
a jar mill, or the like. Mixing may proceed from 15 minutes to 2 hours,
depending on the total amount of salt and the manner of mixing.

[0038]As disclosed in U.S. Pat Pub. No. ______, filed Apr. ______, 2010,
entitled "Thermal Battery Electrolyte Materials, Electrode-Electrolyte
Composites, and Batteries Including Same," which claims the benefit of
U.S. Provisional No. 61/167,040, filed Apr. 6, 2009, which are both
incorporated herein for all relevant and consistent purposes, in addition
to preparing cathodes using the additive in concert with traditional
electrolytes to provide flooding, an additional formulation using a
substantially binder-free electrolyte (that is, containing substantially
no MgO or other binding agent) may be incorporated into the cathode
material to provide additional cathode performance improvement in concert
with the bi-metal sulfide (e.g., CuFeS2) additive. This
substantially binder-free electrolyte may be used as a replacement for
the binder-containing electrolyte conventionally used in thermal
batteries, such as a KCl--LiCl eutectic electrolyte material.

[0039]In this regard it is to be noted that, as used herein, a
"binder-less" electrolyte material (or, alternatively, an electrolyte
material "substantially binder-free") generally refers to an electrolyte
that contains essentially no conventional binder (e.g., MgO, fumed silica
or clay minerals such as kaolinite. For example, in various embodiments,
the electrolyte material may contain less than about 5 wt % binder, less
than about 3 wt %, less than about 1 wt %, less than about 0.1 wt % or
even no amount of binder (based on the total weight of the electrolyte
material). Alternatively or in addition, the sum of the concentrations of
the electrolyte material components (e.g., lithium bromide, lithium
chloride, lithium fluoride, and optionally potassium bromide) may be at
least about 95 wt %, at least about 96 wt %, at least about 97 wt %, at
least about 98 wt %, at least about 99 wt % or even about 100 wt % (based
on the total weight of the electrolyte material). Accordingly, in these
or other embodiments, the electrolyte material may consist, or
alternatively consist essentially of, the recited components (the
electrolyte material being, for example, a ternary mixture of essentially
three components, or a quaternary mixture of essentially four
components).

[0040]Various exemplary substantially binder-free electrolyte materials,
in accordance with various embodiments of the disclosure, include a salt
mixture of lithium bromide (LiBr), lithium chloride (LiCl), lithium
fluoride (LiF), and optionally potassium bromide (KBr). The ratio of the
three or four salts may vary, with preferred embodiments being in the
ranges shown below.

[0041]In this regard it is to be noted that, more generally, the
electrolyte material may contain, in various exemplary embodiments: at
least about 25 wt % lithium bromide, at least about 30 wt %, at least
about 35 wt %, or even at least about 40 wt % lithium bromide; at least
about 4 wt % lithium chloride, at least about 6 wt %, at least about 8 wt
%, at least about 10 wt %, or even at least about 12 wt % lithium
chloride; at least about 42 wt % lithium fluoride, at least about 45 wt
%, at least about 50 wt %, at least about 55 wt %, or even at least about
60 wt % lithium fluoride; and, optionally, at least about 1 wt %
potassium bromide, at least about 2 wt %, at least about 4 wt %, at least
about 8 wt %, or even at least about 10 wt % potassium bromide. It is to
be further noted that, in these or other exemplary embodiments, the
electrolyte material may contain: no more than about 41 wt % lithium
bromide; no more than about 14 wt % lithium chloride; no more than about
64 wt % lithium fluoride; and, when present, no more than about 12 wt %
potassium bromide. Finally, it is to be noted that, in one or more of the
embodiments detailed herein, the concentration of a recited component may
be within a range bounded by any combination or permutation of the higher
and lower concentration limits noted herein (e.g., between about 25 wt %
and about 41 wt %, or between about 30 wt % and about 41 wt % lithium
bromide), without departing from the intended scope of the present
disclosure.

[0042]In preparation of the cathode materials for use in the cathode, the
metal sulfides and/or metal oxides and the bi-metal sulfides may be
purified (if needed) using water and acid washing techniques and magnetic
screening to remove impurities, and as desired may be passed through a
sieve to limit the particle size to some specified range. As described
above in regard to the electrolyte salts, the particle size of the
cathode material should be selected to be consistent with the cell
manufacturing methods of use (e.g., tape casting or pellet pressing) and
moisture should be removed until a level of moisture that does not cause
an unacceptable amount of cell oxidation is achieved. If using powder
pressing for preparation of the cathode material, the mixed powder is
weighed and introduced into a die and consolidated using a uniaxial
mechanical pressing process. While the data presented in the Examples
below is for materials tested using pressed powder pellets, the
application of this material is also possible via means such as tape
casting or other consolidation methods to prepare components for thermal
batteries.

[0043]Once the pressed components are consolidated into pellets, thermal
batteries may be prepared by assembling in stacks the various components
including the anode 102, electrolyte-separator 104, and cathode 106, plus
a heat source pellet 108 if applicable to the particular battery design.
Assembly of one each of anode 102, electrolyte-separator 104, and cathode
106 comprises a single cell. Multiple cells may be stacked in series to
produce a thermal battery. In this regard it should be understood that
thermal battery designs other than as shown in FIG. 1 may be used without
departing from the scope of the present disclosure.

EXAMPLES

[0044]The following examples illustrate the utility of the new cathode
formulation from comparative data of single cell tests. The following
non-limiting examples set forth below are illustrative of various aspects
of certain exemplary embodiments of the present disclosure. The
compositions, methods and various parameters reflected therein are
intended only to exemplify various aspects and embodiments of the
disclosure, and are not intended to limit the scope of the claimed
disclosure.

[0045]FIG. 1 shows a stack arrangement of a thermal battery, including
heat pellet 108 that would be used to melt the electrolyte upon battery
activation. This arrangement, without heat pellet 108, was used for the
single cell tests discussed in the Examples below.

Example 1

Voltage Traces and Impedance for Cells having Non-Lithiated FeS2
Cathodes with and without CuFeS2

[0046]FIG. 2 illustrates voltage traces for two thermal single cells
tested at 500° C., applying a 1 ampere base load with 5 ampere
pulses applied every 60 seconds for a 1 second duration. The first single
cell included a lithium-silicon alloy anode flooded with KCl--LiCl
eutectic electrolyte, a LiBr--LiCl--LiF electrolyte-separator bound with
MgO, and a cathode containing primarily FeS2 (about 63% by weight)
with synthetic CuFeS2 (about 7% by weight) additive that is flooded
with MgO-bound KCl--LiCl eutectic electrolyte making up the remaining 30%
by weight of the cathode pellet. The second thermal single cell contained
the same anode and electrolyte materials, but used a cathode containing
only FeS2 (70% by weight) flooded with the same MgO-bound
electrolyte, hereafter referred to as the "standard cathode." The voltage
of the standard cathode was modified (each data point was subtracted by
0.25 volts) to illustrate the performance of the two cells by avoiding
overlap of the voltage traces. FIG. 3 shows the impedance of the single
cells from the tests shown in FIG. 2. In FIG. 3, the open symbols are for
the single cell using the standard cathode, while the solid symbols are
for the single cell using the FeS2--CuFeS2 cathode formulation
of the present disclosure. The impedance was computed using:

where VBase is the last voltage data under the base load of 1 ampere
prior to application of a pulse, Vpulse is the first data point
after application of the 5 ampere pulse, iBase and iPulse are
the corresponding data points for the current draw for which the
VBase and Vpulse data points were collected. As illustrated in
FIG. 3, the incorporation of the synthetic CuFeS2 additive, keeping
all other components (anode, electrolyte-separator) the same results in a
significant improvement in performance compared to the standard cathode.

Example 2

Voltage Traces and Impedance for Cells having Lithiated FeS2 Cathodes
with and without CuFeS2

[0047]FIG. 4 illustrates a voltage trace for a cathode substantially the
same as the standard cathode of Example 1, but with addition of a
lithiating additive (lithium oxide, Li2O) such that the composition
of the "lithiated standard cathode" is about 70 wt % FeS2, about 2
wt % Li2O, and about 28 wt % MgO-bound KCl--LiCl eutectic
electrolyte. The voltage of the lithiated standard cathode was modified
(each data point was subtracted by 0.25 volts) for illustration purposes.
FIG. 4 also illustrates a voltage trace for a single cell comprised of
the same anode and electrolyte-separator pellet materials described in
Example 1, but using a cathode formulation containing FeS2 (about
58% by weight), naturally-occurring CuFeS2 (about 10% by weight),
Li2O (about 2% by weight), and a substantially binder-free
electrolyte containing KBr, LiBr, LiCl, and LiF (about 30% by weight).
The amount of each salt in the electrolyte material was 10.4 wt % KBr,
35.5 wt % LiBr, 6.4 wt % LiCl and 47.7 wt % LiF.

[0048]FIG. 5 shows the impedance traces for the single cells of FIG. 4.
The open symbols are the data for the single cell using the lithiated
standard cathode, while the solid symbols represent the new cathode
formulation. Different electrolytes and lithiation additives (including
the absence thereof) may be used with the new cathode additive,
regardless of whether the additive is naturally-occurring or synthetic
CuFeS2.

[0049]As can be seen from FIG. 4, the voltage of the new lithiated cell is
sustained and does not "roll-off" until much later in the test as
compared to the standard cathode. As can be seen from FIG. 5, the new
cell has a lower impedance over the entire test as compared to the
standard cell.

Example 3

Voltage Traces and Impedance for Cells having CoS2 Cathodes with and
without CuFeS2

[0050]The test of Example 1 was repeated with CoS2-based cathodes.
One cathode contained CoS2 (about 56% by weight) with synthetic
CuFeS2 (about 14% by weight) additive flooded with MgO-bound
KCl--LiCl eutectic electrolyte making up the remaining 30% by weight of
the cathode pellet. The other cathode contained only CoS2 (70% by
weight) flooded with MgO-bound electrolyte (30% by weight).

[0051]FIG. 6 illustrates voltage traces for the two cells (neither one
being off-set) and FIG. 7 shows the impedance of the single cells. The
open symbols are the data for the single cell using the standard cathode,
while the solid symbols represent the new CoS2--CuFeS2 cathode
formulation. As can be seen in FIGS. 6 and 7, the cathode containing
CuFeS2 additive exhibited superior voltage and impedance
characteristics.

[0052]Various principles of the disclosure have been described in
illustrative embodiments. However, many combinations and modifications of
the above described formulations, proportions, elements, materials, and
components used in the practice of the disclosure, in addition to those
not specifically described, may be varied and particularly adapted to
specific environments and operating requirements without departing from
those principles. Other variations and modifications of the present
disclosure will be apparent to those of ordinary skill in the art, and it
is the intent that such variations and modifications be covered by this
disclosure.

[0053]Further, the description of various embodiments herein makes
reference to the accompanying drawing figures, which show the embodiments
by way of illustration and not of limitation. While these embodiments are
described in sufficient detail to enable those skilled in the art to
practice the disclosure, it should be understood that other embodiments
may be realized and that logical and mechanical changes may be made
without departing from the spirit and scope of the disclosure. Thus, the
disclosure herein is presented for purposes of illustration only and not
of limitation. For example, the steps recited in any of the method or
process descriptions may be executed in any order and are not limited to
the order presented. Moreover, any of the functions or steps may be
outsourced to or performed by one or more third parties. Furthermore, any
reference to singular includes plural embodiments, and any reference to
more than one component may include a singular embodiment.

[0054]Benefits, other advantages, and solutions to problems have been
described herein with regard to specific embodiments. However, the
benefits, advantages, solutions to problems, and any elements that may
cause any benefit, advantage, or solution to occur or become more
pronounced are not to be construed as critical, required, or essential
features or elements of the disclosure. The scope of the disclosure is
accordingly to be limited by nothing other than the claims that may be
included in an application that claims the benefit of the present
application, in which reference to an element in the singular is not
intended to mean "one and only one" unless explicitly so stated, but
rather "one or more." Moreover, where a phrase similar to "at least one
of A, B, and C" may be used in the claims, it is intended that the phrase
be interpreted to mean that A alone may be present in an embodiment, B
alone may be present in an embodiment, C alone may be present in an
embodiment, or that any combination of the elements A, B and C may be
present in a single embodiment; for example, A and B, A and C, B and C,
or A and B and C. Although certain embodiments may have been described as
a method, it is contemplated that the method may be embodied as computer
program instructions on a tangible computer readable carrier and/or
medium, such as a magnetic or optical memory or a magnetic or optical
disk. All structural, chemical, and functional equivalents to the
elements of the above-described embodiments are contemplated within the
scope of this disclosure.

[0055]When introducing elements of the present disclosure or the preferred
embodiments(s) thereof, the articles "a", "an", "the" and "said" are
intended to mean that there are one or more of the elements. The terms
"comprising", "including" and "having" are intended to be inclusive and
mean that there may be additional elements other than the listed
elements.

[0056]As various changes could be made in the above apparatus and methods
without departing from the scope of the disclosure, it is intended that
all matter contained in the above description and shown in the
accompanying figures shall be interpreted as illustrative and not in a
limiting sense.